1. Field of the Invention
The present invention relates to switching apparatus for interconnecting a plurality of incoming and outgoing transmission links in the nodes of a communication network, or for exchanging data between incoming and outgoing computer and workstation connection links. In particular, the apparatus directs circuit switched as well as packet switched traffic from the incoming links selectively to the outgoing links.
2. Description of the Prior Art
Fast switching of information, be it samples of analog signals or alphanumeric data, is an important task in a communication network. The network nodes in which lines or transmission links from various directions are interconnected for exchanging information between them are often the cause of delay in the transmission. If much traffic is concentrated in a node, and if in particular most of the traffic passes through a few of the links, increased delays or even loss of information are encountered.
It is therefore desirable to have switching nodes or exchanges which are fast and practically non-blocking. Such switching nodes should further be able to accommodate different kinds of traffic such as information from circuit switched (CS) voice. channels or data from packet switched (PS) links. Various solutions for exchanges or switching apparatus have been proposed in the literature and in patents.
The article "Integration of Circuit/Packet Switching by a SENET Concept" by G. J. Coviello et al., published in the Proceedings of the National Telecommunications Conference NTC 1975, pp. 42-12 to 42-17 describes a nodal switch for transfer of circuit switched and packet switched information between trunk lines. Input demultiplexers and output multiplexers connect the trunk lines to one common bus for CS traffic and another common bus for PS traffic. Addressed words are transferred sequentially over these busses.
The different handling of PS and CS traffic prevent a uniform internal structure, and the carrying of an address for each single word (i.e. byte) of CS traffic creates much overhead on the bus. Furthermore, a significant portion of the switching functions is done in the multiplexers and demultiplexers which perform TDM switching operations for assigned time slots, each assignment being kept for the duration of the respective CS connection.
U.S. Pat. No. 4,314,367 entitled "Switching Circuit for Digital Packet Switching Network" discloses a switch structure for interconnecting incoming and outgoing links in a packet network node. Each such node switch comprises a two-stage interconnection pattern connecting all inputs to all outputs, and each packet is routed directly from an input to the correct output on the basis of its address. No transfer of circuit switched information is provided as this is a pure packet switching network.
A paper "An Experimental Synchronous Composite Switching System" by T. Takeuchi et al., Proceedings of the IEEE 1986 International Zurich Seminar on Digital Communications, pp. 149-153, describes a switch structure for interconnecting a plurality of trunk lines. The switch basically comprises plural synchronous, slotted transmission rings to which each of the trunks is connected by a switch module. Each switch module can insert addressed packets into empty time slots, and the packets are extracted at the destination switch modules. Both packet switched and circuit switched data can be transferred. However, TDM switching operations with random reordering according to destinations are required separately in each of the trunk switches, and combination of equal switches of this type to configure larger switch systems is not possible.
In German Published Patent Application 2,441,099 entitled, "System zur Vermittlung und Uebertragung digitaler Nachrichten ueber ein Stufenvermittlungsnetzwerk (System for switching and transferring digital messages through a staged switching network)" a packet switching network is disclosed in which each packet has a self-routing address of which each field is associated with a particular node and determines which output is to be taken from that node. This publication does not show the integration of different services and is not suited for transfer of circuit switched information.
The prior art does not show a switching node in which both CS and PS traffic are treated internally equally, and which would allow a modular expansion with equal modules, without requiring higher speed transmission circuitry within the switch modules.